Rohatgi et al, in U.S. Pat. No. 5,626,692, disclose that nickel-coated graphite particles and silicon carbide particles can combine to produce a neutral buoyancy mixture. This neutral buoyancy mixture hinders low-density graphite from floating and high-density silicon carbide particles from sinking in molten aluminum-base matrices. The stability of this molten mixture allows casting of metal matrix composites without special rapid-solidification equipment. This neutral buoyancy method provided the first commercially viable method for casting aluminum-base composites with silicon carbide and graphite particles.
These hybrid silicon carbide-graphite composites provide excellent wear resistance at low cost. Although manufacturers readily machine these hybrid composites, the "hard" silicon carbide particles accelerate tool wear rates of tungsten carbide tools Diamond (PCD and CVD-diamond-coated carbides) have sufficient hardness to machine silicon carbide reinforced metal matrix composites. These diamonds tools however are very expensive, do not resist shocks that occur with interrupted cutting and are only available in limited shapes and sizes. The accelerated wear rates of machining silicon carbide-containing composites can increase machining costs of some applications beyond acceptable limits for certain applications.
It is an object of the invention to form a wear resistant composite.
It is a further object of the invention to provide a composite that facilitates casting without excessive segregation.
It is a further object of this invention to provide a composite that machines with decreased tool wear rates.